1. Field of the Invention
The present invention relates to a fuel injector for use in an internal combustion engine and, more particularly, to a fuel injector for supplying directly the injecting fuel to a respective cylinder of an internal combustion engine in a vehicle such as an automobile.
2. Description of Related Art
In a conventional technique of this kind of a fuel injector for use in an internal combustion engine, the fuel injector has a fuel passage provided upstream of a valve seat. In this fuel injector, a stationary core and a movable core having a valve body are arranged in an axial direction in a yoke and, further, an electromagnetic coil is provided at an inner surrounding portion of the stationary core.
The movable core of the fuel injector is received through the spring force caused by a return spring member. During a non-electric supply of the electromagnetic coil, the valve body is contacted to a valve seat and the valve body is placed in a valve opening condition.
In accordance with electric supply to the electromagnetic coil of the fuel injector, the above stated three components comprised of the stationary core, the yoke, and the movable core form a magnetic circuit. By facing the spring force caused by the return spring member, the movable core is attracted at a side of the stationary core. A valve closing condition in the valve body is then presented.
Further, in the conventional fuel injector, it has been proposed to use a technique in which a swirler is provided at a side upstream of the valve seat of the fuel injector. During the valve opening condition of the valve body, the swirler can give the fuel swirling force to the fuel passing through the swirler and, by swirling the fuel mist, atomizing of the fuel in the fuel injector can be improved and so on.
Among various kinds of fuel injectors, a fuel injector being practiced widely is one having an injection system in which the fuel injector is provided on a part of an air intake passage of an internal combustion of an automobile. However, recently a DI system (a direct injection system) of the fuel injector has been developed; such a DI system is one in which the fuel injector is installed directly to a cylinder of the internal combustion engine and then the fuel is injected directly into the respective cylinder-of the engine.
In the above stated DI system fuel injector, since the fuel is injected directly into the respective cylinder of the engine, it can be estimated that injection is performed without adhesion of the fuel to an inner wall portion of an intake pipe. Further, the injector can provide a good combustion condition having a high efficiency, improve an output of the engine, and further can provide an improvement with respect to an exhaust gas purification.
In a case of DI system fuel injector, as to an aspect to the pressure withstanding property, an interior portion of the cylinder of the engine is placed in a high pressure state in which the pressure reaches about 70 kg/cm.sup.2 at a maximum according to an explosion pressure of the engine. Therefore, there is a problem in that a valve member can be opened erroneously according to surpassing by far the pressure force in the cylinder of the engine against the spring force caused by the return spring member of the fuel injector.
However, recently, according to an improvement of a high pressure pump for supplying the fuel in the fuel injector, the fuel pressure is forced to be high in accordance with cooperation between the fuel pressure and the spring force caused by the return spring member. It is possible to give the valve a closing force which surpasses the above stated explosion pressure force caused by the engine. As a result, the above stated problems about the erroneous valve operation in the fuel injector can be resolved.
Further, as a result of the improvement in the fuel pressure in the fuel injector, since a necessary fuel injection amount can be supplied fully during an extremely limited time such as in an air intake process, a requirement for a responsibility property in the fuel injector can be complied with.
Further, as to an aspect of the responsibility property in the fuel injector, as stated in the above, to surpass the strong valve closing force, a drive electric voltage (a magnetic attraction force) of an electromagnetic coil is heightened using a booster pressure circuit.
To increase the magnetic attraction force in the fuel injector, a drive voltage of the fuel injector is boosted in pressure and a drive current value is increased. In addition, to reduce a consumption electric power for a vehicle such as an automobile, it is necessary to realize a magnetic attraction of the movable core with a high efficiency.
For example, in a fuel injector described in Japanese utility model laid-open publication No. Hei 6-4367, a flange is provided projecting to an upper end face of a side of the magnetic attraction (a side opposite to a lower end face of a stationary core) of a movable core and a tip end of this flange is extended largely toward a lower end face of a yoke. In other words, each of both end portions of the flange of the movable core of the fuel injection is extended over to an outer peripheral portion of the electromagnetic coil.
Accordingly, in this conventional fuel injector, a double gap structure having two gaps in the same horizontal direction to perform the magnetic attraction is provided. Each of the two gaps constituting the double gap structure in the fuel injector is provided at the substantially same horizontal faces and can generate the magnetic attraction force, respectively.
In the above conventional fuel injector, by securing one gap portion in an axial direction between the lower end face of the stationary core and an upper middle face of the flange of the movable core and another gap portion in the axial direction between the lower end face of the yoke and the upper end face of the flange of the movable core, the magnetic attraction area is increased.
However, to increase the magnetic attraction area using the flange provided on the movable core in the conventional fuel injector, the flange is formed to oppose the end face of the stationary core, the lower end face of the electromagnetic coil and the lower end face of the yoke.
As a result, the flange of the movable core is formed with a large outer diameter or the movable core having this flange structure is formed to have the large outer diameter. With such a large outer diameter movable core structure having the large outer diameter flange, an outer diameter of the yoke, which is arranged at an inner surrounding portion of the flange of the movable core, becomes large.
As a result, in the conventional fuel injector, a large size is necessary. Such a large size fuel injector structure is restricted from an aspect of installation for the fuel injector and tends to be a high cost structure.